You’re a physician at a refugee camp in sub-Saharan Africa, when an outbreak of diarrhea occurs. Massive amounts of watery stool, without blood, are produced by the patients. Curved gram-negative rods are seen in a Gram stain of the stool.
Diagnosis: Cholera caused by Vibrio cholerae. There are three genera of curved gram-negative rods: Vibrio, Campylobacter, and Helicobacter. V. cholerae causes watery, nonbloody diarrhea, whereas C. jejuni typically causes bloody diarrhea. Helicobacter pylori causes gastritis and peptic ulcer, not diarrhea. Enterotoxigenic E. coli causes watery diarrhea by producing an exotoxin that has the same mode of action as does the exotoxin produced by V. cholerae. However, E. coli is a straight gram-negative rod, not a curved one. If an outbreak of bloody diarrhea had occurred in the refugee camp, then Shigella dysenteriae would be the most likely cause. See the following pages for additional information: Vibrio, page 156; Campylobacter, page 158; Helicobacter, page 158; Escherichia, page 150; and Shigella, page 155.